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Handle premultiplied alpha modes in ImageColor.getcolor() #9797

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Handle premultiplied alpha modes in ImageColor.getcolor() #9797

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072f1e9
Handle the premultiplied La and RGBa modes in ImageColor.getcolor()
chuenchen309 Jul 17, 2026
16fc5ec
Make LA transform fill opaque, consistent with RGBA
chuenchen309 Jul 19, 2026
3f9d6f1
Remove unrelated assertion
radarhere Jul 19, 2026
89beb8f
Simplified code
radarhere Jul 19, 2026
c96bbf3
Use round()
radarhere Jul 21, 2026
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2 changes: 1 addition & 1 deletion Tests/test_image_transform.py
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,7 @@ def test_quad(self) -> None:
(
("RGB", (255, 0, 0)),
("RGBA", (255, 0, 0, 255)),
("LA", (76, 0)),
("LA", (76, 255)),

@radarhere radarhere Jul 19, 2026

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This check was originally added in #3163

),
)
def test_fill(self, mode: str, expected_pixel: tuple[int, ...]) -> None:
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12 changes: 12 additions & 0 deletions Tests/test_imagecolor.py
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Expand Up @@ -199,6 +199,18 @@ def test_color_hsv() -> None:
assert (170, 255, 255) == ImageColor.getcolor("hsv(240, 100%, 100%)", "HSV")


@pytest.mark.parametrize("mode, premultiplied_mode", (("LA", "La"), ("RGBA", "RGBa")))
@pytest.mark.parametrize("color", ("#f00", "#ff000080", "#ff000050"))
def test_color_premultiplied_alpha(
mode: str, premultiplied_mode: str, color: str
) -> None:
im = Image.new(mode, (1, 1), color)
im_premultiplied = im.convert(premultiplied_mode)
expected = im_premultiplied.getpixel((0, 0))

assert ImageColor.getcolor(color, premultiplied_mode) == expected


def test_color_too_long() -> None:
# Arrange
color_too_long = "hsl(" + "1" * 40 + "," + "1" * 40 + "%," + "1" * 40 + "%)"
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16 changes: 9 additions & 7 deletions src/PIL/ImageColor.py
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Expand Up @@ -152,17 +152,19 @@ def getcolor(color: str, mode: str) -> int | tuple[int, ...]:
r, g, b = rgb
h, s, v = rgb_to_hsv(r / 255, g / 255, b / 255)
return int(h * 255), int(s * 255), int(v * 255)
elif Image.getmodebase(mode) == "L":
if Image.getmodebase(mode) == "L":
r, g, b = rgb
# ITU-R Recommendation 601-2 for nonlinear RGB
# scaled to 24 bits to match the convert's implementation.
graylevel = (r * 19595 + g * 38470 + b * 7471 + 0x8000) >> 16
if mode[-1] == "A":
return graylevel, alpha
return graylevel
elif mode[-1] == "A":
return rgb + (alpha,)
return rgb
value: tuple[int, ...] = (graylevel,)
else:
value = rgb
if mode[-1] == "a":
value = tuple(round(band * alpha / 255) for band in value)
if mode[-1] in ("A", "a"):
return value + (alpha,)
return value[0] if len(value) == 1 else value


colormap: dict[str, str | tuple[int, int, int]] = {
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